The study of airway mechanics in man is usually limited to parameters derived from measurements of pressure, flow and volume. Heretofore, the relationships between function and structure have required indirect assessment of airway dimensions by radiographic techniques. Although these indirect techniques may allow fairly close estimations of airway diameter and length, they are difficult to perform because calibration is often time-consuming and not reproducible. Furthermore, dynamic changes in airway dimensions have been difficult to correlate with dynamic measurements of respiratory function. The introduction of the bronchofiberscope has provided a convenient, minimally invasive technique to observe the glottis and the tracheobronchial tree down to subsegmental bronchi under topical anesthesia. In this proposal an attempt will be made to establish a relationship between structure and function of the intact human airways. The feasibility of transnasal bronchofiberscopy has been established in this and other institutions and we have developed techniques to obtain quantitative measurements of airway dimensions. In addition, the bronchofiberscope enables the placement of pressure probes in selected areas of the upper and lower airways, and the transnasal approach allows simultaneous measurement of pressure, flow and volume by having the subject breathe through a mouthpiece. The temporal integration between visual observations by cinebronchofiberscopy and measurement of dynamic airway mechanics has also been developed in our laboratory. Using these methods, we hope to obtain a better understanding of the interrelationships between structure and function of the upper and lower airways in health and in patients with lung diseases.